Cylindrical Fresnel zone antenna with reflective ground plate

Abstract

An antenna employs cylindrical Fresnel zone plate (CFZP) construction in combination with a reflective ground plate and a sectorial reflector to enhance antenna gain, while lowering assembly cost and improving antenna placement flexibility. By forming a surface of symmetry for the antenna, the ground plate allows the antenna to mimic the operation of a symmetrical CFZP antenna using only half the nominal number of Fresnel elements. Further, the sectorial reflector restricts radiated emissions over a desired sector angle, minimizing radiation in undesirable directions, such as toward mounting walls or other nearby surfaces that would cause unwanted signal reflections, such as might aggravate multipath signal phenomenon.

What is claimed is:  
     
         1 . An antenna comprising: 
 a generally curved dielectric support having inner and outer faces;    a plurality of spaced apart Fresnel elements disposed on the inner face of the dielectric support;    a reflective ground plate positioned adjacent the dielectric support to reflect radiated signals from the plurality of Fresnel elements; and    a feeder positioned at foci of the Fresnel elements.    
     
     
         2 . The antenna of  claim 1 , further comprising a sectorial reflector covering an area of the outer face of the dielectric support.  
     
     
         3 . The antenna of  claim 2 , wherein the feeder comprises a radiating source antenna, and wherein radiated signals from the radiating source antenna are reflected outward from the inner face of the dielectric support by the sectorial reflector and by the Fresnel elements.  
     
     
         4 . The antenna of  claim 1 , wherein the dielectric support extends perpendicularly above the ground plate, and the reflective ground plate defines a plane extending outward from the inner face of the dielectric support.  
     
     
         5 . The antenna of  claim 1 , wherein the dielectric support is cylindrically curved.  
     
     
         6 . The antenna of  claim 5 , wherein the Fresnel elements are cylindrically curved to conform to the inner face of the dielectric support.  
     
     
         7 . The antenna of  claim 5 , further comprising a sectorial reflector positioned on the outer face of the dielectric support, and wherein the sectorial reflector is cylindrically curved to conform to the outer face of the dielectric support.  
     
     
         8 . The antenna of  claim 1 , wherein the dielectric support has a material-dependent thickness of approximately one-quarter wavelength relative to an electromagnetic signal frequency of interest.  
     
     
         9 . The antenna of  claim 1 , wherein the dielectric support comprises at least a portion of a right circular cylinder.  
     
     
         10 . The antenna of  claim 9 , wherein the Fresnel elements each comprise at least a portion of a right circular cylindrical ring.  
     
     
         11 . The antenna of  claim 1 , wherein the ground plate comprises a conductive wire mesh.  
     
     
         12 . The antenna of  claim 1 , wherein each Fresnel element comprises a series of segments joined to approximate a generally curved ring.  
     
     
         13 . The antenna of  claim 1 , wherein a maximum segment length for the series of segments is chosen such that the joined segments substantially conform to a curvature of the inner face of the dielectric support.  
     
     
         14 . The antenna of  claim 1 , wherein a width of each Fresnel element is a function of the distance of the Fresnel element from the reflective ground plate.  
     
     
         15 . The antenna of  claim 14 , wherein the width is measured from a bottom edge of the Fresnel element to a top edge of the Fresnel element relative to the reflective ground plate.  
     
     
         16 . The antenna of  claim 14 , wherein the widths of the Fresnel elements decrease with increasing distance from the reflective ground plate.  
     
     
         17 . The antenna of  claim 1 , wherein one or more of the Fresnel elements comprises a plurality of joined segments.  
     
     
         18 . The antenna of  claim 1 , wherein the dielectric support comprises a plurality of joined segments.  
     
     
         19 . An antenna comprising: 
 a reflective ground plate;    a cylindrically curved dielectric support extending above the ground plate;    a plurality of spaced apart Fresnel elements disposed on an inner face of the dielectric support;    a feeder element adjacent to the ground plate at foci of the Fresnel elements; and    an electromagnetic reflector disposed on an outer face of the dielectric support, and covering at least a portion of the outer face over a desired cylindrical sector angle.    
     
     
         20 . The antenna of  claim 19 , wherein the dielectric support has a material-dependent thickness that is approximately one-quarter wavelength of an electromagnetic signal frequency of interest, such that the Fresnel elements and the electromagnetic reflector are separated by approximately a material-dependent one-quarter wavelength for the frequency of interest.  
     
     
         21 . The antenna of  claim 19 , wherein the dielectric support comprises a sector of a right circular cylinder having a first sector angle.  
     
     
         22 . The antenna of  claim 21 , wherein the Fresnel elements each comprise a sector of a cylindrical band having second sector angles.  
     
     
         23 . The antenna of  claim 22 , wherein the first sector angle of the dielectric support is greater than the second sector angles of the Fresnel elements.  
     
     
         24 . The antenna of  claim 22 , wherein the first sector angle of the dielectric support is less than the second sector angle of the Fresnel elements.  
     
     
         25 . The antenna of  claim 22 , wherein the dielectric support is a right circular cylinder, such that the first sector angle is  360  degrees.  
     
     
         26 . The antenna of  claim 25 , wherein the Fresnel elements are complete cylindrical hoops spaced apart on the inner face of the dielectric support.  
     
     
         27 . The antenna of  claim 25 , wherein the Fresnel elements are incomplete cylindrical hoops spaced apart on the inner face of the dielectric support.  
     
     
         28 . The antenna of  claim 19 , wherein the Fresnel elements comprise a first plurality of Fresnel elements, and wherein the ground plate is a reflective ground plate acting as a surface of symmetry for the antenna, such that the antenna mimics a second plurality of Fresnel elements.  
     
     
         29 . The antenna of  claim 19 , wherein the feeder comprises a monopole antenna.  
     
     
         30 . The antenna of  claim 19 , wherein the feeder comprises a dipole antenna.  
     
     
         31 . The antenna of  claim 19 , wherein the feeder comprises a microstrip patch antenna.  
     
     
         32 . The antenna of  claim 19 , wherein the feeder comprises an electromagnetic source, such that electromagnetic energy radiated from the feeder is reflected outward relative to the inner face of the dielectric support by a combination of the Fresnel elements and the reflector.  
     
     
         33 . The antenna of  claim 32 , wherein the reflector substantially blocks electromagnetic radiation over the desired cylindrical sector angle behind the outer face of the dielectric support.  
     
     
         34 . The antenna of  claim 19 , wherein each of the Fresnel elements comprises a series of segments joined to form a least a portion of a cylindrically curved ring.  
     
     
         35 . The antenna of  claim 34 , wherein a maximum segment length of each segment is limited such that the cylindrically curved ring substantially conforms to the cylindrically curved dielectric support.  
     
     
         36 . The antenna of  claim 19 , wherein the ground plate comprises a conductive material.  
     
     
         37 . The antenna of  claim 36 , wherein the conductive material is a wire mesh.  
     
     
         38 . The antenna of  claim 36 , wherein the conductive material comprises a metallic plate.  
     
     
         39 . The antenna of  claim 19 , wherein a width of each Fresnel element is a function of the distance of the Fresnel element from the reflective ground plate.  
     
     
         40 . The antenna of  claim 39 , wherein the width is measured from a bottom edge of the Fresnel element to a top edge of the Fresnel element relative to the reflective ground plate.  
     
     
         41 . The antenna of  claim 39 , wherein the widths of the Fresnel elements decrease with increasing distance from the reflective ground plate.  
     
     
         42 . The antenna of  claim 19 , wherein each Fresnel element comprises a series of joined segments.  
     
     
         43 . The antenna of  claim 19 , wherein the dielectric support comprises a series of joined segments.  
     
     
         44 . The antenna of  claim 19 , wherein the reflector comprises a series of joined segments.